Yes, apparently they do. Looking at a 22 tooth, however, I can't see how there's room for the bolt holes to go any smaller. But I guess they figured it out.
Unfortunately, the inexpensive steel 20's only come in 58 BCD. The only option is titanium at $60.
Since its apparently possible to do, why doesn't Shimano make a 20?

Many full suspension frames were engineered around the middle ring being 32-34 and the majority of pedaling being done in that ring. Pedaling in granny is not ideal on my Nomad and induces pedal feedback. Riding a 31 home brewed sprocket and 11-36 XT/ebay 9 speed cassette here. Riding San Diego's finest in the front and rear on my bike. Living in San Diego...

Yes, apparently they do. Looking at a 22 tooth, however, I can't see how there's room for the bolt holes to go any smaller. But I guess they figured it out.
Unfortunately, the inexpensive steel 20's only come in 58 BCD. The only option is titanium at $60.
Since its apparently possible to do, why doesn't Shimano make a 20?

I wonder the same thing! Anyone have any experience with the 20T on a 64mm bolt spacing? I used to have one on my old 5-arm crank, but it's hard to see how something that small would fit on a 4-arm crank.

I currently run a 1X9 with a 32T chainring and 11-34 cog. I am climbing just fine with the 32/34 but my problem is I am spinning out on the flats. If i were to get the 12-36 cog I would change the front ring to a 34....

Now that's overkill... you might have trouble staying on the bike at very low speeds.

Because everyone rides the same as you, has the same fitness level as you, and rides the same terrain as you?

The hardest thing for me with super low gearing is that the momentum is not as strong when the trail is chunky. Steep non-tech trails have not been a problem at super low speeds in that regard. Anything that can help you keep pedaling instead of walking or stopping is a good thing. I have used some super low gearing setups in the past for several years. Even if one can eventually get fit enough to not need it, it may help them get to that point faster if they can keep moving, even if it is not real fast.

Originally Posted by edubfromktown

I have 11-34 cassette with 38/32/20 rings (compact 94/58 cranks) on a 29er which is plenty low 'n slow for any significant grade & duration climb.

$himano doesn't make 20t in 94/58 or anything else for the same reason they are phasing out 9-speed... so you will chuck what you have and buy new stuff.

Shimano doesn't make a 20t in 58mm BCD, but others do (or have) besides actiontec. Race Face made a 20t with 58mm BCD in steel and they were excellent and very durable. You can still find them from time to time on ebay. Salsa is another, but those are/were aluminum and not nearly as durable as the steel ones from Race Face.

Originally Posted by edubfromktown

The HG-61 will munch your freehub body/drive shell for sure. The 36t cog makes for a lot of torque... Smaller chain rings and with less exotic (and lighter) cassettes is a much better approach.

I'm curious to know if the freehub cares how the torque/hp is manufactured? It seems like it takes what it takes to keep your body/bike (mass) moving up a steep hill at a given speed. If your legs have the power to climb with a combination that yields x gear inches, how does it matter to the freehub how you arrive at the final drive ratio?

I currently run a 1X9 with a 32T chainring and 11-34 cog. I am climbing just fine with the 32/34 but my problem is I am spinning out on the flats. If i were to get the 12-36 cog I would change the front ring to a 34....

Unfortunately that 1 tooth change on the low end has a big enough effect that 34x12 is actually a slower gear than 32x11. A 36t ring would give you a faster top end gear ratio but actually only by a small amount compared to 32x11

I'm curious to know if the freehub cares how the torque/hp is manufactured? It seems like it takes what it takes to keep your body/bike (mass) moving up a steep hill at a given speed. If your legs have the power to climb with a combination that yields x gear inches, how does it matter to the freehub how you arrive at the final drive ratio?

I think I know what you are saying. The torque would be the force applied by the chain times the radius of the gear, FxR. The torque will only be enough to move the wheel, so if R goes up, F goes down, and torque stays the same with a larger cog. The potential torque is greater with a larger cog, for example if the wheel was held still while applying max force to the chain. But if you stay within your same power outputs while the wheel is rolling, using a larger cog wouldn't put more torque on the freehub. (that's what I'm thinking anyway).

I currently run a 1X9 with a 32T chainring and 11-34 cog. I am climbing just fine with the 32/34 but my problem is I am spinning out on the flats. If i were to get the 12-36 cog I would change the front ring to a 34....

I wonder the same thing! Anyone have any experience with the 20T on a 64mm bolt spacing? I used to have one on my old 5-arm crank, but it's hard to see how something that small would fit on a 4-arm crank.

I run a 21 tooth and hubby runs a 20, both Action Tec ti. His rear is 11-30 mine is 11-32. They work very well! I have been considering running a 1x9 with a 11-36 but not until they get the weight down and give us more options.

I wonder the same thing! Anyone have any experience with the 20T on a 64mm bolt spacing? I used to have one on my old 5-arm crank, but it's hard to see how something that small would fit on a 4-arm crank.

I can't find the picture I saw, but I think the bolt hole takes up part of the space of a tooth, so there is a little mini tooth above the hole. Hard to describe.

170mm cranks + steep hills= 12-36 cassette

I ran a 1x9 on my old bike, I race cross country on an 11-32, but I run a 12-36 on my AM bike and I love it.

If your AM bike is on the FR side, then you are most likely on 170mm cranks. If you are on more of a FR bike, then you probably live somewhere with very very steep hills. If this is you, 12-36 is the only way to go.

It is so nice being able to sit and comforably spin up the hill like a normal person. The tiny weight penalty of the 12-36 is of course totally invisible, the added gearing however will change your life.

The downside is that the bigger cassette will tend to dig into your aluminum freehub body and get really stuck. I just took one off this morning and it was a pain in the ass.

So the torque on the freehub does matter, because if you look at what things are constant in a bike drivetrain, you can basically assume that max chain tension in a given pedal stroke is usually some fairly constant value, because it is a function of force at the pedal and the size of your chainring. This larger chain tension being applied to a larger cog would induce a greater torque at the freehub, even while yielding the same final drive ratio. This is assuming that the pedal force remains fairly constant, which in my experience/perception is not that outlandish.

Good info. Thanks!

I ran a 1x9 on my old bike, I race cross country on an 11-32, but I run a 12-36 on my AM bike and I love it.

If your AM bike is on the FR side, then you are most likely on 170mm cranks. If you are on more of a FR bike, then you probably live somewhere with very very steep hills. If this is you, 12-36 is the only way to go.

It is so nice being able to sit and comforably spin up the hill like a normal person. The tiny weight penalty of the 12-36 is of course totally invisible, the added gearing however will change your life.

The downside is that the bigger cassette will tend to dig into your aluminum freehub body and get really stuck. I just took one off this morning and it was a pain in the ass.

The cassette and lockring is 423g on my scale.

great thread, as i am currently trying to figure this out.

So for instance, i currently own a 11-34. if i remove the 11 or 12T and install that 36T from either the shimano or the EBAY 36T, i will have problems with rubbing? or you will only encounter issues if you install the 12-36 cassette "CS-HG61"?

You can transmit maximum torque to the freehub for a given chain tension in your largest cassette gear ergo larger gears dig more into soft aluminum freehubs than smaller ones. Caveat, I can dig a fifteen tooth, the only free narrow cog on an XT 11-34, thoroughly into a DT 240 FH with little apparent effort so it's not like it matters to me.

20T Granny : $20 (64 BCD)

I switched to a 20T granny a year ago and never looked back. Now my knees don't hurt on super steep climbs (anyone heard of Pumphouse Hill and Hell Hill?). Run it with the PG990 11-34 cassette and its my Secret Weapon for hills.

This guy is selling them on Ebay for $20: eBay My World - crmxer or just search 20T chainring, it should pop up.

He makes them out of stainless steel at his machine shop and I must say they work very well. The secret is out now...

I switched to a 20T granny a year ago and never looked back. Now my knees don't hurt on super steep climbs (anyone heard of Pumphouse Hill and Hell Hill?). Run it with the PG990 11-34 cassette and its my Secret Weapon for hills.

This guy is selling them on Ebay for $20: eBay My World - crmxer or just search 20T chainring, it should pop up.

He makes them out of stainless steel at his machine shop and I must say they work very well. The secret is out now...

You can transmit maximum torque to the freehub for a given chain tension in your largest cassette gear ergo larger gears dig more into soft aluminum freehubs than smaller ones. Caveat, I can dig a fifteen tooth, the only free narrow cog on an XT 11-34, thoroughly into a DT 240 FH with little apparent effort so it's not like it matters to me.

For any given speed, wouldn't the torque on the hub be the same regardless of of gear sizes? That would have to be true to obey the conservation of energy law, right? For example, a small cog with large chain ring requires more chain tension but a smaller lever arm on the hub, while a large cog with small chain ring results in a larger lever arm, but with a lower force, to produce the same speed.

Some of the steep climbs in Idaho were too difficult on my Niner W.F.O. with a 22-23-44 front with a 11-34 on the back cassette. I put the 12-36 on the rear and have not noticed the extra weight. I have noticed easier climbing and better control on loose gravel/sand on the climbs. I have not tried swapping the 12 tooth for an eleven, but it sounds like it works fine!

Some of the steep climbs in Idaho were too difficult on my Niner W.F.O. with a 22-23-44 front with a 11-34 on the back cassette. I put the 12-36 on the rear and have not noticed the extra weight. I have noticed easier climbing and better control on loose gravel/sand on the climbs. I have not tried swapping the 12 tooth for an eleven, but it sounds like it works fine!

Hey guys..first post so guess I'll jump in! After over a decade in Porsche and aviation forums I feel like I'm cheating on my friends, but think I'll be putting most all my online time into this new forum. Quit wrenching on antique 911's and quit flying professionally. So here I be now!

I'm curious how the swap from the 12 to an 11 worked on your cassette? Is it a clunky shift between 8 and 9 or smooth enough? I think they both jump to a 14t next cog up. I'm upgrading soon from 8-sp SRAM X.4 to 9-sp X.5 shifters, and from a SRAM 11-32 cass to a shimano 12-36. Are you able to interchange individual cogs like that? Also hoping my Shimano M475 rear hub will handle more torque from the larger cogs. I'd read I may need a M529 that's 29er specific.

I'm curious how the swap from the 12 to an 11 worked on your cassette? Is it a clunky shift between 8 and 9 or smooth enough? I think they both jump to a 14t next cog up. I'm upgrading soon from 8-sp SRAM X.4 to 9-sp X.5 shifters, and from a SRAM 11-32 cass to a shimano 12-36. Are you able to interchange individual cogs like that? Also hoping my Shimano M475 rear hub will handle more torque from the larger cogs. I'd read I may need a M529 that's 29er specific.

The 12 to the 11 switch should not be a problem. As long as it is the same brand you should be ok with the spacing (shimano?) and the shifting should be the same.

As for the rear hub handling the load, I have had problems this year with blowing out the freehub on the 29er with a 20T up front and a 11-36 cassette. I believe this equates to a lower ratio than some of the 26/42 set ups I've seen out there and the torque has destroyed two hubs this year alone. I weigh about 225lbs and the problem happens on grades around +22% with technical climbing on rocks (lots of traction).

I also broke a few chains on these trails with this set up. The feeling of almost going over the bars when the hub or chain fails has now retired this 29er to being just my trail bike, and I do all my tech-climbing on my 26 again with a Mavic Crossmax wheelset. I am not sure about the hub you have, but I do have a shimano on one of my bikes and had no problems.